SPONGES. 31 



the rock, you could exhibit the phenomenon to him at work in 

 a shallow dish of sea-water. Thereupon he, thinking to be of 

 service to you tears off a slice of the pale green? hillocky 

 sponge (Halichoiidria panicca) and breaks it up hopelessly. 

 However, we will turn his clumsiness to account and take a 

 view of the interior thus violently exposed. We see that these 

 crater-like openings are the outlets to tubular spaces running 

 through the sponge, and from these passages smaller branches 

 go off at right angles, whilst these and the larger openings are 

 surrounded by tissues that are very like bread in consistence ; 

 and that is really only a way of explaining that they are 

 spongy. Now the whole of the substance of these sponges, as 

 you may see by microscopical examination, is composed of 

 myriads of minute flint spicules, finer than the most delicate 

 fragments of " spun-glass," and of beautiful forms. Some are 

 simple rods, straight and curved ; others forked at one end ; 

 some like a gribble ; others what is known as quadriradiate in 

 form. 



Now in some species these spicules are not arranged in any 

 order; they are merely jumbled together, and their remarkable 

 forms make it easy for them to become entangled. When so en- 

 tangled they form the skeleton of the sponge. Each sponge is 

 a co-operative colony containing many thousands of members, 

 and these are represented to our view, through my pocket 

 lens, in the mass only, as a thin clear jelly investing the 

 spicule-tangles, or rather the spicules are imbedded in the 

 sarcode as this living matter is termed. If we were to chip off 

 a thin flake of rock with its investing sponge intact, and place 

 the whole in a glass vessel full of water, we could observe the 

 movements which manifest its vitality. A little finely powdered 

 indigo or other colouring matter should be dropped into the 

 water near the specimen. On closely observing it would be 

 seen that many of these minute granules were flowing towards 

 the sponge, then that they entirely disappeared through the 

 very fine openings in the surface. A little later these particles 



